Extractive Distillation of Crude Alcohol Product

ABSTRACT

Recovery of ethanol from a crude ethanol product obtained from the hydrogenation of acetic acid using an extractive distillation column. The column yields a residue that comprises ethanol, acetic acid, and the extractive agent. The extractive agent may be water and may be separated from the residue and returned to the extractive distillation column.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingethanol from acetic acid in a hydrogenation reactor and, in particular,to an extractive distillation process for recovering ethanol.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulose materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosematerial, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulose materials competes with food sources and placesrestraints on the amount of ethanol that can be produced for industrialuse.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacid, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition whenconversion is incomplete, unreacted acid remains in the crude ethanolproduct, which must be removed to recover ethanol.

EP2060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

Others have proposed various extractive agents for separating mixturesof ethanol, ethyl acetate and water. U.S. Pat. No. 4,654,123 describes aprocess for separating ethanol from water using extractive agents. U.S.Pat. Nos. 4,379,028 and 4,569,726 describe processes for recoveringethyl acetate from an ethyl acetate/ethanol/water mixture usingextractive agents. U.S. Pat. No. 6,375,807 describes a method ofseparating ethanol and ethyl acetate using extractive agents.

The need remains for improved processes for recovering ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor producing ethanol comprising the steps of hydrogenating acetic acidfrom an acetic acid feed stream in a reactor to form a crude ethanolproduct comprising ethanol, ethyl acetate, and acetic acid; separatingat least a portion of the crude ethanol product in a first column in thepresence of one or more extractive agents into a first distillatecomprising ethyl acetate, and a first residue comprising ethanol, aceticacid, and the one or more extractive agents; and recovering ethanol fromthe first residue. The extractive agent may also be recovered from thefirst residue and returned to the first column.

The one or more extractive agents are selected from a group consistingof water, dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol,hydroquinone, N,N′-dimethylformamide, 1,4-butanediol, ethyleneglycol-1,5-pentanediol, propylene glycol-tetraethyleneglycol-polyethylene glycol, glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane, N,N′dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine, diethylenetriamine, hexamethylene diamine, 1,3-diaminopentane, and alkylatedthiopene, dodecane, tridecane, tetradecane, chlorinated paraffins, andmixtures thereof.

In a second embodiment, the present invention is directed to a processfor producing ethanol comprising the steps of providing a crude ethanolproduct comprising ethanol, acetic acid, and ethyl acetate; separatingat least a portion of the crude ethanol product in a first column in thepresence of one or more extractive agents into a first distillatecomprising ethyl acetate, and a first residue comprising ethanol, aceticacid, and the one or more extractive agents; and recovering ethanol fromthe first residue.

In a third embodiment, the present invention is directed to a processfor producing ethanol comprising the steps of hydrogenating acetic acidfrom an acetic acid feed stream in a reactor to form a crude ethanolproduct comprising ethanol, ethyl acetate, water, and acetic acid;feeding an extractive agent comprising water and at least a portion ofthe crude ethanol product to a first column; separating at least aportion of the crude ethanol product in a first column into a firstdistillate comprising ethyl acetate, and a first residue comprisingethanol, acetic acid, and water; and recovering the extractive agentfrom the first residue.

In a fourth embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid from anacetic acid feed stream in a reactor to form a crude ethanol productcomprising ethanol, and ethyl acetate, separating at least a portion ofthe crude ethanol product in a first column in the presence of one ormore extractive agents into a first distillate comprising ethyl acetate,and a first residue comprising ethanol, and the one or more extractiveagents, and recovering ethanol from the first residue.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, wherein like numeralsdesignate similar parts.

FIG. 1 is a schematic diagram of an ethanol production system withdistillation columns to recover the extractive agent, water, from aceticacid in accordance with one embodiment of the present invention.

FIG. 2 is a schematic diagram of an ethanol production system withdistillation columns to recover the extractive agent, water, fromethanol in accordance with one embodiment of the present invention.

FIG. 3 is a schematic diagram of an ethanol production system withdistillation columns to recover the extractive agent, water, inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Introduction

The present invention relates to processes for recovering ethanolproduced by hydrogenating acetic acid in the presence of a catalyst. Thehydrogenation reaction produces a crude ethanol product that comprisesethanol, water, ethyl acetate, unreacted acetic acid, and otherimpurities. Ethyl acetate is difficult to separate from a mixture ofethyl acetate and ethanol by distillation because of the closeness inboiling points between ethyl acetate and ethanol. The presence of othercomponents in the crude ethanol product such as ethyl acetate, aceticacid and acetaldehyde, depending on concentration, may furthercomplicate the separation of ethanol and ethyl acetate.

To improve efficiencies in recovering ethanol from the crude ethanolproduct, the processes of the present invention involve recoveringethanol from the crude ethanol product using one or more extractiveagents in an initial (first) separation column. Ethanol, water, andacetic acid are withdrawn as the residue. Ethyl acetate and other lightorganics are withdrawn as the distillate. Specifically, the presentinvention provides processes for separating ethyl acetate and ethanolfrom the crude ethanol product in an initial separation column using oneor more extractive agents. By using one or more extractive agents, anethanol product may be recovered having a reduced ethyl acetate content.In addition, the use of one or more extractive agents may beneficiallyreduce the energy required to recover ethanol with low amounts of ethylacetate.

The presence of the extractive agents allows the ethanol product to beseparated from the ethyl acetate by-product more effectively. Using anextractive agent in accordance with embodiments of the present inventionallows for a majority of the ethyl acetate to be recovered from thecrude ethanol product. Preferably, at least 90% of the ethyl acetate inthe crude ethanol product is recovered through the first distillate,e.g., at least 95% of the ethyl acetate or at least 98% of the ethylacetate. Recovering a majority of the ethyl acetate provides for lowconcentrations of ethyl acetate in the residue from the initial column,e.g., less than 1 wt. %, less than 0.3 wt. % or less than 0.01 wt. %.Thus, it is not necessary to engage in additional separations of ethanoland ethyl acetate when recovering ethanol from the residue.

Advantageously, this separation approach results in reducing energyrequirements to recover ethanol from the crude ethanol product.

The extractive agent preferably has a boiling point higher than majorcomponents in the distillate. In preferred embodiments, the extractiveagent employed has a boiling point greater than 80° C., e.g., greaterthan 85° C., or greater than 100° C. Extractive agents having boilingpoints greater than 200° C. are also contemplated. A preferredextractive agent comprises water. The water may be produced in thehydrogenation reactor and recycled as the extractive agent. Othersuitable extractive agents include, for example, dimethylsulfoxide,glycerine, diethylene glycol, 1-naphthol, hydroquinone,N,N′-dimethylformamide, 1,4-butanediol, ethylene glycol-1,5-pentanediol,propylene glycol-tetraethylene glycol-polyethylene glycol,glycerine-propylene glycol-tetraethylene glycol-1,4-butanediol, ethylether, methyl formate, cyclohexane, N,N′ dimethyl-1,3-propanediamine,N,N′-dimethylethylenediamine, diethylene triamine, hexamethylenediamine, 1,3-diaminopentane, and alkylated thiopene, dodecane,tridecane, tetradecane and chlorinated paraffins. These other agents maybe used with water. Some suitable extraction agents include thosedescribed in U.S. Pat. Nos. 4,379,028; 4,569,726; 5,993,610; and6,375,807, the entireties of which are incorporated herein by reference.

In one embodiment, the extractive agents may be fed to the initialcolumn for processing the crude ethanol product. In another embodiment,the extractive agents are fed to and combined with the crude ethanolproduct prior to being introduced into the initial column. Preferably, asubstantial portion of the ethanol, water, and acetic acid is removedfrom the crude ethanol product as the residue from the initial column.The residue stream, for example, may comprise from 30 to 90% of thewater and from 85% to 100% of the acetic acid from the crude ethanolproduct. The residue stream may also comprise the extractive agent,water, and thus the water concentration in the residue may exceed thewater concentration of the crude ethanol product. The extractive agentsmay be recovered from the residue, e.g., in one or more additionalseparation columns, and recycled to the initial column.

Generally, the distillate from the initial column may comprise ethylacetate and acetaldehyde. The distillate may be recycled in whole orpart to the hydrogenation reactor. In some embodiments, the distillatefrom the initial column may also comprise ethanol and preferably lessthan 15 wt. % water, less than 7.5 wt. % water, less 4 wt. % water orless than 2 wt. % water. In one embodiment, a light ends column may beused to further separate the distillate into ethyl acetate stream, whichis recycled to the hydrogenation reactor, and ethanol stream.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. The materials, catalysts, reactionconditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from more available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from a variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also U.S. Pub. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a by-product of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid fed to the hydrogenation reaction may also compriseother carboxylic acids and anhydrides, as well as acetaldehyde andacetone. Preferably, a suitable acetic acid feed stream comprises one ormore of the compounds selected from the group consisting of acetic acid,acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof.These other compounds may also be hydrogenated in the processes of thepresent invention. In some embodiments, the presence of carboxylicacids, such as propanoic acid or its anhydride, may be beneficial inproducing propanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 kPato 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 1500 kPa.The reactants may be fed to the reactor at a gas hourly space velocity(GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹, greaterthan 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms of ranges theGHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Suitable hydrogenationcatalysts include catalysts comprising a first metal and optionally oneor more of a second metal, a third metal or any number of additionalmetals, optionally on a catalyst support. The first and optional secondand third metals may be selected from Group IB, IIB, IIIB, IVB, VB,VIIB, VIIB, VIII transition metals, a lanthanide metal, an actinidemetal or a metal selected from any of Groups IIIA, IVA, VA, and VIA.Preferred metal combinations for some exemplary catalyst compositionsinclude platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, cobalt/tin,silver/palladium, copper/palladium, copper/zinc, nickel/palladium,gold/palladium, ruthenium/rhenium, and ruthenium/iron. Exemplarycatalysts are further described in U.S. Pat. No. 7,608,744 and U.S. Pub.No. 2010/0029995, the entireties of which are incorporated herein byreference. In another embodiment, the catalyst comprises a Co/Mo/Scatalyst of the type described in U.S. Pub. No. 2009/0069609, theentirety of which is incorporated herein by reference.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium. More preferably, the first metal is selected fromplatinum and palladium. In embodiments of the invention where the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another or may comprise a non-alloyedmetal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When present, the total weight of the thirdmetal preferably is from 0.05 to 4 wt. %, e.g., from 0.1 to 3 wt. %, orfrom 0.1 to 2 wt. %.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %,or from 1 to 8 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a supportmodifier. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,and Al₂O₃. The acidic modifier may also include WO₃, MoO₃, Fe₂O₃, Cr₂O₃,V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint-Gobain NorPro. The Saint-GobainNorPro SS61138 silica exhibits the following properties: containsapproximately 95 wt. % high surface area silica; surface area of about250 m²/g; median pore diameter of about 12 nm; average pore volume ofabout 1.0 cm³/g as measured by mercury intrusion porosimetry and apacking density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheresfrom Sud Chemie having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a molepercentage based on acetic acid in the feed. The conversion may be atleast 10%, e.g., at least 20%, at least 40%, at least 50%, at least 60%,at least 70% or at least 80%. Although catalysts that have highconversions are desirable, such as at least 80% or at least 90%, in someembodiments a low conversion may be acceptable at high selectivity forethanol. It is, of course, well understood that in many cases it ispossible to compensate for conversion by appropriate recycle streams oruse of larger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, the selectivity to ethanolis at least 80%, e.g., at least 85% or at least 88%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%. More preferably, these undesirableproducts are present in undetectable amounts. Formation of alkanes maybe low, and ideally less than 2%, less than 1%, or less than 0.5% of theacetic acid passed over the catalyst is converted to alkanes, which havelittle value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseunreacted acetic acid, ethanol and water. As used herein, the term“crude ethanol product” refers to any composition comprising from 5 to70 wt. % ethanol and from 5 to 40 wt. % water. Exemplary componentsranges of the crude ethanol are provided in Table 1. The othercomponents identified in Table 1 may include, for example, esters,ethers, aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 70 15 to 70  15to 50 25 to 50 Acetic Acid 0 to 90 0 to 50 15 to 70 20 to 70 Water 5 to40 5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30 0 to 20  1 to 12  3to 10 Acetaldehyde 0 to 10 0 to 3  0.1 to 3  0.2 to 2  Others 0.1 to 10 0.1 to 6   0.1 to 4  —

In one embodiment, the crude ethanol product comprises acetic acid in anamount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt. %or less than 5 wt. %. In embodiments having lower amounts of aceticacid, the conversion of acetic acid is preferably greater than 75%,e.g., greater than 85% or greater than 90%. In addition, the selectivityto ethanol may also be preferably high, and is preferably greater than75%, e.g., greater than 85% or greater than 90%.

In one embodiment, the weight ratio of ethanol to water may be at least0.18:1 or greater, e.g., at least 0.5:1 or at least 1:1. In terms ofranges the weight ratio of ethanol to water may be from 0.18:1 to 5:1,e.g., from 0.5:1 to 3:1 or from 1:1 to 2:1. Preferably the crude ethanolproduct has more ethanol than water compared to conventionalfermentation processes of ethanol. In one embodiment, the lower amountsof water may require less energy to separate the ethanol and improvesthe overall efficiency of the process. Thus, in preferred embodiments,the amount of ethanol in the crude ethanol product is from 15 wt. % to70 wt. %, e.g., from 20 wt. % to 70 wt. % or from 25 wt. % to 70 wt. %.Higher ethanol weight percents are particularly preferred.

Ethanol Recovery

Exemplary ethanol recovery systems in accordance with embodiments of thepresent inventions are shown in FIGS. 1-3. Each hydrogenation system 100includes a suitable hydrogenation reactor and a process for separatingethanol from the resulting crude ethanol mixture. System 100 comprisesreaction zone 101 and separation zone 102. For purposes of describingsystem 100 the extractive agent used in FIGS. 1-3 is water. Inseparation zone 102 for FIG. 1, the extractive agent is separated fromacetic acid. FIG. 2, the extractive agent is separated from ethanolafter removing acetic acid. In FIG. 3, the extractive agent is separatedfrom ethanol without separately removing acetic acid. System 100 shownin FIG. 3 may be suitable for high acetic acid conversion where thecontent of acetic acid is low.

Reaction zone 101 comprises reactor 103, hydrogen feed line 104 andacetic acid feed line 105. Hydrogen and acetic acid are fed to avaporizer 110 via lines 104 and 105, respectively, to create a vaporfeed stream in line III that is directed to reactor 103. In oneembodiment, lines 104 and 105 may be combined and jointly fed to thevaporizer 110, e.g., in one stream containing both hydrogen and aceticacid. The temperature of the vapor feed stream in line III is preferablyfrom 100° C. to 350° C., e.g., from 120° C. to 310° C. or from 150° C.to 300° C. Any feed that is not vaporized is removed from vaporizer 110,as shown in FIG. 1, and may be recycled or discarded. In addition,although FIG. 1 shows line 111 being directed to the top of reactor 103,line 111 may be directed to the side, upper portion, or bottom ofreactor 103. Further modifications and additional components to reactionzone 101 and separation zone 102 are described below.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid, to ethanol. In oneembodiment, one or more guard beds (not shown) may be used upstream ofthe reactor, optionally upstream of vaporizer 110, to protect thecatalyst from poisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol product stream is withdrawn, preferablycontinuously, from reactor 103 via line 112.

The crude ethanol product stream in line 112 may be condensed and fed toa separator 106, which, in turn, provides a vapor stream 114 and aliquid stream 113. The separator 106, for example, may comprise one ormore flashers or knockout pots. The separator 106 may operate at atemperature of from 20° C. to 250° C., e.g., from 30° C. to 225° C. orfrom 60° C. to 200° C. The pressure of separator 106 may be from 50 kPato 2000 kPa, e.g., from 75 kPa to 1500 kPa or from 100 kPa to 1000 kPa.Optionally, the crude ethanol product in line 112 may pass through oneor more membranes to separate hydrogen and/or other non-condensablegases.

The vapor stream 114 exiting separator 106 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101. Asshown, vapor stream 114 is combined with the hydrogen feed 104 andco-fed to vaporizer 110. In some embodiments, the returned vapor stream114 may be compressed before being combined with hydrogen feed 104.

The liquid stream 113 from separator 106 is withdrawn and pumped tofirst column 107, also referred to as an “extractive column.”

In one embodiment, the contents of liquid stream 113 are substantiallysimilar to the crude ethanol product obtained from the reactor, exceptthat the composition has been depleted of hydrogen, carbon dioxide,methane and/or ethane, which are preferably removed by separator 106.Accordingly, liquid stream 113 may also be referred to as a crudeethanol product. Exemplary components of liquid stream 113 are providedin Table 2. It should be understood that liquid stream 113 may containother components, not listed in Table 2.

TABLE 2 LIQUID STREAM 113 Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Ethanol 5 to 70    10 to 60 15 to 50 Acetic Acid <90  0.01 to 80  1 to70 Water 5 to 40    5 to 30 10 to 30 Ethyl Acetate <30  0.001 to 20  1to 12 Acetaldehyde <10 0.001 to 3 0.1 to 3  Acetal <5 0.001 to 2 0.005to 1    Acetone <5  0.0005 to 0.05 0.001 to 0.03  Other Esters <5 <0.005<0.001 Other Ethers <5 <0.005 <0.001 Other Alcohols <5 <0.005 <0.001

The amounts indicated as less than (<) in the tables throughout presentapplication are preferably not present and if present may be present intrace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol or mixtures thereof. In one embodiment, the liquid stream 113,may comprise propanol, e.g., isopropanol and/or n-propanol, in an amountfrom 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from 0.001 to 0.03wt. %. It should be understood that these other components may becarried through in any of the distillate or residue streams describedherein and will not be further described herein, unless indicatedotherwise.

Optionally, crude ethanol product in line 112 or in liquid stream 113may be further fed to an esterification reactor, hydrogenolysis reactor,or combination thereof. An esterification reactor may be used to consumeacetic acid present in the crude ethanol product to further reduce theamount of acetic acid to be removed. Hydrogenolysis may be used toconvert ethyl acetate in the crude ethanol product to ethanol.

Liquid stream 113 is introduced in the upper part of first column 107,e.g., upper half or upper third. As shown, one or more extractiveagents, as described above, are also introduced to column 107 via line115 to aid with the separation of ethanol from water (and othercomponents). Preferably, the extractive agent is recovered directly orindirectly from the first residue and recycled back to first column 107,as shown in FIGS. 1 and 2, optionally with the addition of freshextractive agent as indicated by 125. The extractive agent is preferablyintroduced near the top of the column and flows downward until itreaches the reboiler. The extractive agent in line 115 ideally isintroduced above the feed point of the liquid stream 113.

The amount of extractive agent fed to extractive column 107 may varywidely. For example, when the extractive agent in line 115 compriseswater, the mass flow ratio of water to crude ethanol product may rangefrom 2:1 to 1:15, e.g., from 1:1.1 to 1:12 or from 1:1.2 to 1:10.

The crude ethanol product in liquid stream 113 comprises ethyl acetate,ethanol and water. These compounds may form various binary and tertiaryazeotropes. For example, a tertiary azeotrope may have a boiling pointlower than its constituents, while other tertiary azeotropes may have aboiling point in between the pure constituents. In the embodiments ofthe present invention, without the use of an extractive agent, a largerportion of the ethyl acetate would leak into the first residue in line116. By using an extractive agent in column 107, the separation ofethanol into the first residue in line 116, with minimal amounts ofethyl acetate, is facilitated thus increasing the yield of the overallethanol product in the first residue in line 116.

In this manner, ethanol water, unreacted acetic acid, and other heavycomponents, if present, are removed from the liquid stream 113 and arewithdrawn, preferably continuously, as first residue in line 116. Firstcolumn 107 also forms a first distillate, which is withdrawn in line117, and which may be condensed and refluxed, for example, at a ratio offrom 30:1 to 1:30, e.g., from 10:1 to 1:10 or from 5:1 to 1:5.

When column 107 is operated under about 170 kPa, the temperature of theresidue exiting in line 116 preferably is from 70° C. to 155° C., e.g.,from 90° C. to 130° C. or from 100° C. to 110° C. The temperature of thedistillate exiting in line 117 preferably is from 30° C. to 100° C.,e.g., from 60° C. to 85° C. or from 65° C. to 80° C. In someembodiments, the pressure of first column 107 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplarycompositions of the first distillate and the first residue for firstcolumn 107 are provided in Table 3 below. It should also be understoodthat the distillate and residue may also contain other components, notlisted in Table 3. For convenience, the distillate and residue of thefirst column may also be referred to as the “first distillate” or “firstresidue.” The distillates or residues of the other columns may also bereferred to with similar numeric modifiers (second, third, etc.) inorder to distinguish them from one another, but such modifiers shouldnot be construed as requiring any particular separation order.

TABLE 3 EXTRACTIVE COLUMN 107 Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)First Distillate Ethanol <20 0.1 to 15 0.5 to 10  Water  1 to 30  2 to25 4 to 15 Acetic Acid   <0.2 <0.01 not detectable Ethyl Acetate 35 to95  35 to 80 35 to 60  Acetaldehyde <35 0.1 to 30 5 to 30 Acetal <35 0.1to 30 5 to 30 First Residue Acetic Acid 0.1 to 50  0.5 to 40 1 to 30Water 40 to 85  50 to 80 55 to 75  Ethanol 10 to 80  15 to 60 15 to 45 Ethyl Acetate   <1.0 <0.3  <0.01

Water in the residue includes both the water produced in thehydrogenation reactor that is present in the crude ethanol product andwater fed to column 107 as the extractive agent 115. As more water isfed as the extractive agent, the amount of water in the residue willincrease. The increase in amount of extractive agent fed may alsofurther decrease the leakage of ethyl acetate in the first residue. Forexample, the ethyl acetate concentration in the first residue may bevery low and may range from 1 wppm to 800 wppm and more preferably from5 wppm to 250 wppm.

In an embodiment of the present invention, column 107 utilizes anextractive agent to aid in the separation of ethyl acetate and ethanol.Thus, most of the ethanol, water, and acetic acid are removed from theresidue stream and only a small amount of ethanol and water is collectedin the distillate stream. The weight ratio of ethanol in the residue inline 116 to ethanol in the distillate in line 117 may be greater than1:1, e.g., greater than 2:1. The weight ratio of water in the residue tothe water in the distillate may be greater than 1:1, e.g., greater than2:1.

Some species, such as acetals, may decompose in first column 107 suchthat very low amounts, or even no detectable amounts, of acetals remainin the distillate or residue. In addition, an equilibrium reactionbetween acetic acid and ethanol or between ethyl acetate and water mayoccur in the crude ethanol product after it exits the reactor 103.Depending on the concentration of acetic acid in the crude ethanolproduct, this equilibrium may be driven toward formation of ethylacetate. This equilibrium may be regulated using the residence timeand/or temperature of crude ethanol product.

As shown in FIG. 1, the residue stream 116 is introduced to a secondcolumn 108, also referred to as an “acid separation column,” becauseacid, if any, from the first residue 116 is removed in second column108. An acid separation column may be used when the acetic acidconcentration in the first residue is greater than 1 wt. %, e.g.,greater than 5 wt. %. In some embodiments, when the acetic acidconcentration is low, e.g., less than 10 wt. %, the water separationcolumn in FIG. 3 may be used.

In FIG. 1, the first residue in line 116 is introduced to second column108, preferably in the middle part of column 108, e.g., middle half ormiddle third. Second column 108 yields a second residue in line 118comprising acetic acid and water, and a second distillate in line 119comprising ethanol. Second column 108 may be a tray column or packedcolumn. In one embodiment, second column 108 is a tray column havingfrom 5 to 150 trays, e.g., from 15 to 50 trays or from 20 to 45 trays.Although the temperature and pressure of second column 108 may vary,when at atmospheric pressure the temperature of the second residueexiting in line 118 from second column 108 preferably is from 95° C. to130° C., e.g., from 100° C. to 125° C. or from 110° C. to 120° C. Thetemperature of the second distillate exiting in line 119 from secondcolumn 108 preferably is from 60° C. to 105° C., e.g., from 75° C. to100° C. or from 80° C. to 100° C. The pressure of second column 108 mayrange from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPato 375 kPa. Exemplary components for the distillate and residuecompositions for second column 108 are provided in Table 4 below. Itshould be understood that the distillate and residue may also containother components, not listed in Table 4.

TABLE 4 ACID SEPARATION COLUMN 108 (FIG. 1) Conc. (wt. %) Conc. (wt. %)Conc. (wt. %) Second Distillate Ethanol  70 to 99.9    75 to 98  80 to95 Ethyl Acetate <10  0.001 to 5 0.01 to 3  Acetaldehyde <5 0.001 to 10.005 to 0.5  Water 0.1 to 30    1 to 25  5 to 20 Second Residue AceticAcid 0.1 to 45   0.2 to 40 0.5 to 35 Water  45 to 100     55 to 99.8  65to 99.5 Ethyl Acetate <2 <1 <0.5 Ethanol <5 0.001 to 5 <2  

The weight ratio of ethanol in the second distillate in line 119 toethanol in the second residue in line 118 preferably is at least 35:1.In one embodiment, the weight ratio of water in the second residue 118to water in the second distillate 119 is greater than 2:1, e.g., greaterthan 4:1 or greater than 6:1. In addition, the weight ratio of aceticacid in the second residue 118 to acetic acid in the second distillate119 preferably is greater than 10:1, e.g., greater than 15:1 or greaterthan 20:1. Preferably, the second distillate in line 119 issubstantially free of acetic acid and may only contain, if any, traceamounts of acetic acid. A reduced concentration of acetic acid in line119 advantageously provides an ethanol product that also has no amountor a trace amount of acetic acid. Preferably, the second distillate inline 119 contains substantially no ethyl acetate. The second distillatein line 119 may be withdrawn as the ethanol product or further processedto reduce water concentration.

In FIG. 1, to recover the water as the extractive agent for use in firstcolumn 107, the second residue in line 118 is further separated into awater stream and an acetic acid stream. As shown in FIG. 1 there isprovided a distillation column, however, other separation units, such asa membrane, may be used to separate second residue in line 118. Thesecond residue in line 118 is introduced to a third column 109,preferably in the top part of column 109, e.g., top half or top third.The third distillate in line 121 preferably comprises water and very lowamount of acetic acid, e.g., less than 1 wt. %, or less than 0.5 wt. %.The third distillate in line 121 may be returned to first column 107 asextractive agent in line 115 or may be purged as necessary.

Third column 109 may be a tray column or packed column. In oneembodiment, third column 109 is a tray column having from 5 to 150trays, e.g., from 15 to 50 trays or from 20 to 45 trays. Although thetemperature and pressure of third column 109 may vary, when atatmospheric pressure the temperature of the third residue exiting inline 120 preferably is from 115° C. to 140° C., e.g., from 120° C. to135° C. or from 125° C. to 135° C. The temperature of the thirddistillate exiting in line 121 at atmospheric pressure preferably isfrom 90° C. to 110° C., e.g., from 95° C. to 110° C. or from 100° C. to110° C. The pressure of third column 109 may range from 0.1 kPa to 510kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

In other embodiments of the present invention, acetic acid and water maybe separated using membranes, adsoprtions, reactive distillation column,azeotropic distillation, and others as described herein. Depending onthe amount of water and acetic acid contained in the third residue ofthird column 109, third residue in line 120 may be treated in one ormore of the following processes. The following are exemplary processesfor further treating third residue and it should be understood that anyof the following may be used regardless of acetic acid concentration.When the residue comprises a majority of acetic acid, e.g., greater than70 wt. %, the residue may be recycled to the reactor without anyseparation of water. In one embodiment, the residue may be separatedinto an acetic acid stream and a water stream when the residue comprisesa majority of acetic acid, e.g., greater than 50 wt. %. Acetic acid mayalso be recovered in some embodiments from third residue having a loweracetic acid concentration. The residue may be separated into the aceticacid and water streams by a distillation column or one or moremembranes. If a membrane or an array of membranes is employed toseparate the acetic acid from the water, the membrane or array ofmembranes may be selected from any suitable acid resistant membrane thatis capable of removing a permeate water stream. The resulting aceticacid stream optionally is returned to reactor 103. The resulting waterstream may be used as an extractive agent or to hydrolyze anester-containing stream in a hydrolysis unit.

In other embodiments, for example where third residue in line 120comprises less than 50 wt. % acetic acid, possible options include oneor more of: (i) returning a portion of the third residue to reactor 103,(ii) neutralizing the acetic acid, (iii) reacting the acetic acid withan alcohol, or (iv) disposing of the third residue in a waste watertreatment facility. It also may be possible to separate second and/orthird residue comprising less than 50 wt. % acetic acid using a weakacid recovery distillation column to which a solvent (optionally actingas an azeotroping agent) may be added. Exemplary solvents that may besuitable for this purpose include ethyl acetate, propyl acetate,isopropyl acetate, butyl acetate, vinyl acetate, diisopropyl ether,carbon disulfide, tetrahydrofuran, isopropanol, ethanol, and C₃-C₁₂alkanes. When neutralizing the acetic acid, it is preferred that thethird residue in line 120 comprises less than 10 wt. % acetic acid.Acetic acid may be neutralized with any suitable alkali or alkalineearth metal base, such as sodium hydroxide or potassium hydroxide. Whenreacting acetic acid with an alcohol, it is preferred that the residuecomprises less than 50 wt. % acetic acid. The alcohol may be anysuitable alcohol, such as methanol, ethanol, propanol, butanol, ormixtures thereof. The reaction forms an ester that may be integratedwith other systems, such as carbonylation production or an esterproduction process. Preferably, the alcohol comprises ethanol and theresulting ester comprises ethyl acetate. Optionally, the resulting estermay be fed to the hydrogenation reactor.

In some embodiments, when the third residue comprises very minor amountsof acetic acid, e.g., less than 5 wt. %, the third residue may bedisposed of to a waste water treatment facility without furtherprocessing. The organic content, e.g., acetic acid content, of thesecond distillate beneficially may be suitable to feed microorganismsused in a waste water treatment facility.

The acid separation column may also be operated in a manner thatwithdraws a second residue that comprises acetic acid and a seconddistillate that comprises ethanol and water. In FIG. 2, second column122 may be a tray column or packed column. In one embodiment, secondcolumn 122 is a tray column having from 5 to 70 trays, e.g., from 15 to50 trays or from 20 to 45 trays. When column 122 is operated understandard atmospheric pressure, the temperature of the residue exiting inline 123 preferably is from 95° C. to 130° C., e.g., from 105° C. to117° C. or from 110° C. to 115° C. The temperature of the distillateexiting in line 124 from column 107 preferably is from 70° C. to 110°C., e.g., from 75° C. to 95° C. or from 80° C. to 90° C. In otherembodiments, the pressure of first column 107 may range from 0.1 KPa to510 KPa, e.g., from 1 KPa to 475 KPa or from 1 KPa to 375 KPa. Exemplarycomponents for the distillate and residue compositions for second column122 are provided in Table 5 below.

TABLE 5 ACID SEPARATION COLUMN 122 (FIG. 2) Conc. (wt. %) Conc. (wt. %)Conc. (wt. %) Distillate Ethanol 10 to 85 15 to 45 20 to 40 Water 10 to90 50 to 80 60 to 80 Acetic Acid <2 0.001 to 0.5  0.01 to 0.2  EthylAcetate   <0.5 <0.01 0.001 to 0.01  Acetaldehyde <2 <0.01 0.001 to 0.01 Residue Acetic Acid  60 to 100  65 to 100 85 to 95 Water <30  0.5 to 30  1 to 15 Ethanol <1 <0.9  <0.07

The second residue in line 123 may be recycled to reaction zone 101 ortreated as discussed above to remove water.

As shown in FIG. 2, the remaining water, if any, from the seconddistillate in line 124 may be removed in further embodiments of thepresent invention. Depending on the water concentration, the ethanolproduct may be derived from the second distillate in line 124. Someapplications, such as industrial ethanol applications, may toleratewater in the ethanol product, while other applications, such as fuelapplications, may require an anhydrous ethanol. Water may be removedfrom the second distillate in line 124 using several differentseparation techniques. Particularly preferred techniques include the useof distillation column, membranes, adsorption units and combinationsthereof.

As shown, the second distillate in line 124 is fed to a third column126, e.g., ethanol product column, for separating the distillate into athird distillate (ethanol distillate) in line 128 and a third residue(water residue) in line 127. The third residue in line 127 or a portionthereof may be returned to first column 107 as an extractive agent.Depending on the amount of water needed as the extractive agent aportion of third residue in line 127 may also be purged. Seconddistillate in line 124 may be introduced into the lower part of column126, e.g., lower half or lower third. Third distillate 128 preferably isrefluxed, for example, at a reflux ratio of from 1:10 to 10:1, e.g.,from 1:3 to 3:1 or from 1:2 to 2:1. Third column 126 is preferably atray column as described above and preferably operates at atmosphericpressure. The temperature of the third distillate exiting from thirdcolumn 126 preferably is from 60° C. to 110° C., e.g., from 70° C. to100° C. or from 75° C. to 95° C. The temperature of the third residue inline 127 preferably is from 70° C. to 115° C., e.g., from 80° C. to 110°C. or from 85° C. to 105° C., when the column is operated at atmosphericpressure. Exemplary components of the distillate and residuecompositions for third column 126 are provided in Table 6 below. Itshould be understood that the distillate and residue may also containother components, not listed, such as components in the feed.

TABLE 6 ETHANOL PRODUCT COLUMN 126 Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Distillate Ethanol 75 to 96   80 to 96  85 to 96 Water <12   1to 9  3 to 8 Acetic Acid <1 0.001 to 0.1 0.005 to 0.01 Ethyl Acetate <50.001 to 4  0.01 to 3  Residue Water 75 to 100   80 to 100  90 to 100Ethanol   <0.8 0.001 to 0.5 0.005 to 0.05 Ethyl Acetate <1 0.001 to 0.50.005 to 0.2  Acetic Acid <2 0.001 to 0.5 0.005 to 0.2 

As indicated above, when acid conversion is high in reactor 103, onecolumn may be used to recover the ethanol product and water as theextractive agent. In FIG. 3 the first residue in line 116 is fed to asecond column 129, referred to as the “water recovery column.” The waterfrom first residue in line 116 may be separated into the second residuein line 132 and returned to first column 107. There may be some aceticacid in second residue in line 132 and purge 133 may be taken asnecessary.

In FIG. 3, the first residue in line 116 is introduced to the top partof second column 129, e.g., top half or top third. Although thetemperature and pressure of second column 129 may vary, when atatmospheric pressure the temperature of the second residue exiting inline 132 preferably is from 70° C. to 120° C., e.g., from 90° C. to 115°C. or from 95° C. to 110° C. The temperature of the second distillateexiting in line 131 preferably is from 15° C. to 100° C., e.g., from 15°C. to 70° C. or from 40° C. to 70° C. The pressure of second column 129may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1kPa to 375 kPa. Exemplary components for the distillate and residuecompositions for second column 129 are provided in Table 7 below.

TABLE 7 WATER RECOVERY COLUMN 129 Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Distillate Ethanol 70 to 96 80 to 93 85 to 93 Water  5 to 30  5 to 20 5 to 15 Acetaldehyde <30 0.01 to 10  0.01 to 5   Ethyl Acetate   <1.5<1 <0.01 Residue Water 90 to 99 92 to 99 95 to 99 Ethanol  <5 0.001 to2    0.005 to 1    Acetic Acid  1 to 10 1 to 6 1 to 5

Returning to the first distillate in line 117, which comprises ethylacetate and/or acetaldehyde, preferably is refluxed as shown in FIG. 1,for example, at a reflux ratio of from 1:30 to 30:1, e.g., from 1:5 to5:1 or from 1:3 to 3:1. In one aspect, not shown, the first distillateor a portion thereof may be returned to reactor 103. In someembodiments, it may be advantageous to return a portion of firstdistillate to reactor 103. The ethyl acetate and/or acetaldehyde fromthe first distillate may be further reacted in hydrogenation reactor 103or in a secondary reactor. The outflow from the secondary reactor may befed to reactor 103 to produce additional ethanol or to a distillationcolumn to recover additional ethanol.

In some embodiments, the first distillate in line 117 may also compriseminor amounts of water. If all or a portion of the first distillate isreturned to the reactor, it may be necessary to remove water from line117. The water from the first distillate in line 117 may be removed, forexample, by an adsorption unit, one or more membranes, molecular sieves,extractive distillation, or a combination thereof. For example, anadsorption unit (not shown) may be used to remove a water stream fromfirst distillate in line 117 thus producing a refined light streampreferably comprising less than 1 wt. % water and more preferably lessthan 0.5 wt. % water. Adsorption unit may remove up to 99.99% of thewater from the first distillate in line 117, and more preferably from95% to 99.99% of the water from the first distillate. Refined lightstream, or a portion thereof, may be returned to reactor 103.

In one embodiment, the first distillate in line 117, or a portion ofeither or both streams, may be further separated to produce anacetaldehyde-containing stream and an ethyl acetate-containing stream.This may allow a portion of either the acetaldehyde-containing stream orethyl acetate-containing stream to be recycled to reactor 103, whilepurging the other stream. The purge stream may be valuable as a sourceof either ethyl acetate and/or acetaldehyde.

The columns used in the present invention may comprise any distillationcolumn capable of performing the desired separation and/or purification.Each column preferably comprises a tray column having from 1 to 150trays, e.g., from 10 to 100 trays, from 20 to 95 trays or from 30 to 75trays. The trays may be sieve trays, fixed valve trays, movable valvetrays, or any other suitable design known in the art. In otherembodiments, a packed column may be used. For packed columns, structuredpacking or random packing may be employed. The trays or packing may bearranged in one continuous column or they may be arranged in two or morecolumns such that the vapor from the first section enters the secondsection while the liquid from the second section enters the firstsection, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As apractical matter, pressures from 10 kPa to 3000 kPa will generally beemployed in these zones although in some embodiments subatmosphericpressures or superatmospheric pressures may be employed. Temperatureswithin the various zones will normally range between the boiling pointsof the composition removed as the distillate and the composition removedas the residue. As will be recognized by those skilled in the art, thetemperature at a given location in an operating distillation column isdependent on the composition of the material at that location and thepressure of column. In addition, feed rates may vary depending on thesize of the production process and, if described, may be genericallyreferred to in terms of feed weight ratios.

Distillate in lines 119, 128, and 131 comprise ethanol, as discussedabove, and may be further purified to form an anhydrous ethanol productstream, i.e., “finished anhydrous ethanol,” using one or more additionalseparation systems, such as, for example, distillations (e.g., afinishing column), pressure swing absorption system, membrane, molecularsieves, extractive distillation, or a combination thereof.

Any of the compounds that are carried through the distillation processfrom the feed or crude reaction product generally remain in the ethanoldistillate in amounts of less 0.1 wt. %, based on the total weight ofthe ethanol distillate composition, e.g., less than 0.05 wt. % or lessthan 0.02 wt. %. In one embodiment, one or more side streams may removeimpurities from any of the columns in the system 100. Preferably atleast one side stream is used to remove impurities from the thirdcolumn. The impurities may be purged and/or retained within the system100.

The final ethanol composition obtained by the process of the presentinvention may be taken from the third distillate or optionally from thesecond distillate. The ethanol product may be an industrial gradeethanol comprising 75 to 96 wt. % ethanol, e.g., from 80 to 96 wt. % orfrom 85 to 96 wt. % ethanol, based on the total weight of the finishedethanol composition. Exemplary finished ethanol compositional ranges areprovided below in Table 8.

TABLE 8 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05<0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

In some embodiments, when further water separation is used, the ethanolproduct may be withdrawn as a stream from the water separation unit asdiscussed above. In such embodiments, the ethanol concentration of theethanol product may be greater than indicated in Table 6, and preferablyis greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greaterthan 99.5 wt. %. The ethanol product in this aspect preferably comprisesless than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogenation transport or consumption.In fuel applications, the finished ethanol composition may be blendedwith gasoline for motor vehicles such as automobiles, boats and smallpiston engine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may esterified with acetic acid. In anotherapplication, the finished ethanol composition may be dehydrated toproduce ethylene. Any known dehydration catalyst can be employed todehydrate ethanol, such as those described in copending U.S. Pub. Nos.2010/0030002 and 2010/0030001, the entire contents and disclosures ofwhich are hereby incorporated by reference. A zeolite catalyst, forexample, may be employed as the dehydration catalyst. Preferably, thezeolite has a pore diameter of at least about 0.6 nm, and preferredzeolites include dehydration catalysts selected from the groupconsisting of mordenites, ZSM-5, a zeolite X and a zeolite Y. Zeolite Xis described, for example, in U.S. Pat. No. 2,882,244 and zeolite Y inU.S. Pat. No. 3,130,007, the entireties of which are hereby incorporatedherein by reference.

In order that the invention disclosed herein may be more efficientlyunderstood, an example is provided below. It should be understood thatthis example is for illustrative purposes only and is not to beconstrued as limiting the invention in any manner.

Example 1

The following examples were prepared with ASPEN Plus™ V7.1 simulationsoftware to test various feed composition and separation systems.

A crude ethanol product comprising 56 wt. % ethanol, 38 wt. % water, 2%acetaldehyde, 2% ethyl acetate, 1 wt. % acetic acid, and 1 wt. % otherorganics is fed to column. This column contains 75 trays with theextractive agent feed location at the 1st tray from the top and crudeethanol product feed location at the 14th tray from the top. The flowrate of the crude ethanol product is 341502 lb/hr. The reflux rate is 11times the distillate rate. The distillate temperature was about 65° C.and the residue temperature was about 103° C. to 107° C. The pressure ofthe column was 170.3 kPa. The distillate and residue compositions forthree separate runs are shown in Table 9. Run A was without anyextractive agent feed at a location above the crude ethanol product.Runs B and C used water as an extractive agent.

TABLE 9 Run A Run B Run C Extractive Agent flow rate 0 125,000 250,000(lb/hr) Distillate (wt. %) Ethanol 25.0 0.6 1.9 Water 6.0 7.4 6.3 EthylAcetate 31.2 37.5 37.2 Acetic Acid <0.01 <0.01 <0.01 Acetaldehyde 27.327.3 27.3 Other organics 10.5 27.3 27.3 Residue (wt. %) Ethanol 57.842.7 33.3 Water 39.9 56.6 66.1 Ethyl Acetate 0.4 <0.01 <0.01 Acetic Acid1.0 0.7 0.6 Acetaldehyde <0.01 <0.01 <0.01 Other organics 1.0 <0.01<0.01 % of Ethanol Recovered in 97.5 99.9 99.8 Residue % of EthylAcetate 82.5 99.6 99.9 Recovered in Distillate Energy (MMBtu per ton of0.73 0.80 1.02 ethanol refined) Ethyl Acetate Leakage in 3863 59 12residue (wppm)

For Runs B and C, the presence of an extractive agent, allowed fordecreased amounts of ethyl acetate leakage into the residue over Run A.In addition, higher ethanol recovery rates were demonstrated in Runs Band C based on the ASPEN simulation.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

1. A process for producing ethanol, comprising: hydrogenating aceticacid from an acetic acid feed stream in a reactor to form a crudeethanol product comprising ethanol, ethyl acetate, and acetic acid;separating at least a portion of the crude ethanol product in a firstcolumn in the presence of one or more extractive agents into a firstdistillate comprising ethyl acetate, and a first residue comprisingethanol, acetic acid, and the one or more extractive agents; andrecovering ethanol from the first residue.
 2. The process of claim 1,wherein the one or more extractive agents are selected from a groupconsisting of water, dimethylsulfoxide, glycerine, diethylene glycol,1-naphthol, hydroquinone, N,N′-dimethylformamide, 1,4-butanediol,ethylene glycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane, N,N′dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine, diethylenetriamine, hexamethylene diamine, 1,3-diaminopentane, and alkylatedthiopene, dodecane, tridecane, tetradecane, chlorinated paraffins, andmixtures thereof.
 3. The process of claim 1, wherein the first residuecomprises less than 1 wt. % ethyl acetate.
 4. The process of claim 1,further comprising the steps of separating the first residue in one ormore distillation columns to recover the extractive agent.
 5. Theprocess of claim 1, further comprising the steps of separating the firstresidue in a second column into a second distillate comprising ethanol,and a second residue comprising the one or more extractive agents andacetic acid.
 6. The process of claim 5, further comprising the steps ofseparating the second residue in a third column into a third distillatecomprising the one or more extractive agents, and a third residuecomprising acetic acid.
 7. The process of claim 1, further comprisingthe steps of separating the first residue in a second column into asecond distillate comprising ethanol and the one or more extractiveagents, and a second residue comprising acetic acid.
 8. The process ofclaim 7, further comprising the steps of separating the seconddistillate in a third column into a third distillate comprising ethanol,and a third residue comprising the one or more extractive agents.
 9. Theprocess of claim 1, wherein the one or more extractive agents are addedabove the portion of the crude ethanol product fed to the first column.10. The process of claim 1, wherein the one or more extractive agentsare co-produced in the reactor.
 11. The process of claim 1, wherein theacetic acid is formed from methanol and carbon monoxide, wherein each ofthe methanol, the carbon monoxide, and hydrogen for the hydrogenatingstep is derived from syngas, and wherein the syngas is derived from acarbon source selected from the group consisting of natural gas, oil,petroleum, coal, biomass, and combinations thereof.
 12. A process forproducing ethanol, comprising the steps of: providing a crude ethanolproduct comprising ethanol, acetic acid, and ethyl acetate; separatingat least a portion of the crude ethanol product in a first column in thepresence of one or more extractive agents into a first distillatecomprising ethyl acetate, and a first residue comprising ethanol, aceticacid, and the one or more extractive agents; and recovering ethanol fromthe first residue.
 13. The process of claim 12, wherein the firstresidue comprises less than 1 wt. % ethyl acetate.
 14. A process forproducing ethanol, comprising the steps of: hydrogenating acetic acidfrom an acetic acid feed stream in a reactor to form a crude ethanolproduct comprising ethanol, ethyl acetate, water, and acetic acid;feeding an extractive agent comprising water and at least a portion ofthe crude ethanol product to a first column; separating at least aportion of the crude ethanol product in a first column into a firstdistillate comprising ethyl acetate, and a first residue comprisingethanol, acetic acid, and water; and recovering the extractive agentfrom the first residue.
 15. The process of claim 14, wherein the firstresidue comprises less than 1 wt. % ethyl acetate.
 16. The process ofclaim 14, wherein the recovered extractive agent is returned to thefirst column.
 17. The process of claim 14, further comprising the stepsof separating the first residue in a second column into a seconddistillate comprising ethanol, and a second residue comprising water andacetic acid.
 18. The process of claim 17, further comprising the stepsof separating the second residue in a third column into a thirddistillate comprising water, and a third residue comprising acetic acid.19. The process of claim 14, further comprising the steps of separatingthe first residue in a second column into a second distillate comprisingethanol and water, and a second residue comprising acetic acid.
 20. Theprocess of claim 19, further comprising the steps of separating thesecond distillate in a third column into a third distillate comprisingethanol, and a third residue comprising water.
 21. A process forproducing ethanol, comprising: hydrogenating acetic acid from an aceticacid feed stream in a reactor to form a crude ethanol product comprisingethanol, and ethyl acetate; separating at least a portion of the crudeethanol product in a first column in the presence of one or moreextractive agents into a first distillate comprising ethyl acetate, anda first residue comprising ethanol, and the one or more extractiveagents; and recovering ethanol from the first residue.